Prior U.S. Pat. No. 3,125,917 discloses a punch and die assembly comprising upper and lower plates or templets serving to positionally locate the upper and lower ends of punch and die elements in supported engagement with punch and die shoes, respectively; an intermediate plate or templet fixed to the die shoe via lower portions of shoe guide device and serving to positionally locate the dies of the die elements; and a moveable plate means or locater templet means movably suspended below the punch shoe via upper portions of the punch shoe guide devices and carrying a plurality of guide elements or buttons having openings sized to slideably receive the punching or tip ends of the punch elements in order to orient same relative to their associated dies. Stripper devices in the form of coil type compression springs dispose concentrically of the die elements for opposite end bearing engagement with a lower surface of the upper plate and an upper surface of an associated guide button. The spring devices, working through the guide buttons, additionally function to normally bias removable plate means to bottom out against an abutment defined by upper portions of a shoe guide devices.
In one embodiment of the assembly, lower surfaces of the guide buttons project below a lower surface of the moveable plate means for stripping engagement with a workpiece.
The moveable plate means is illustrated and described as including two or more identical plates or templets, which are clamped in surface-to-surface engagement and appear to individually be of a thickness corresponding to that of the upper, lower and intermediate plates; such thickness being such as to permit punch forming of the guide or locater aperatures in such plates. Apparently, as workpieces of increasing thickness are to be punched, the number of plates comprising the moveable plate means must be increased for stiffening purposes.
Applicant became aware of U.S. Pat. No. 3,125,917 as a result of prosecution of his above mentioned patent application, and subsequently conducted tests in an effort to compare the performance capabilities of the patented system with those of the system disclosed in his application.
In that the patented system was not available for test purposes, Applicant's system was modified in an effort to simulate operational conditions of the patented system. In this respect, Applicant's die set was modified by removing stripper sleeves 138, and by modifying pin support devices 82, such that they supported templet 80 to position guide elements or buttons 90 in essential surface-to-surface abutting engagement with the lower ends of stripper sleeves 60, when the punch shoe 20 is disposed in an operative or die set open condition. As modified, pin supports 82 and stripper sleeves 60 are believed to functionally replace the abutment device defined by said screw 47 and shoulder 40 and stripping springs 65 of the system disclosed in U.S. Pat. No. 3,125,917.
For reference test purposes, die set illustrated in Applicant's application was set up to insure that the spacing between guide sleeves 126 and guide bushings 132 permitted compression of stripper sleeves 138 no later than stripper sleeves 60, when a stock or workpiece thickness of 0.1 inch was being punched; this dictating that the initial spacing of approximately 0.1 inch is present between the bottom of stripper sleeves 60 and the upper surfaces of their associated guide buttons 90, when the latter are fully seated relative to templet 80.
A series of four reference tests were conducted with first and second tests using 0.001 inch thick stock or workpiece material and differing from one another only in that in a first test the stock was "full-sized" to permit all punches to be simultaneously operative and in a second test the stock was "half-sized", so that only one half of the punches arranged on one side or half of the die set were operative. The third and fourth tests were conducted using 0.1 inch thick stock or workpiece material with the "full and half sized" punching conditions of the first and second tests being repeated, respectively. Results of the referenced tests demonstrated the substantially increased accuracy described in Applicant's patent application.
A series of four comparison tests were conducted using Applicant's die set modified in the manner described above with stock thicknesses and sizes identical to those used in the referenced tests. In conducting the comparison tests, the same punch and die elements were used, as those used in the referenced tests; such punch and die elements having been inspected prior to conducting the comparison tests and no damage or wear being noted as a result of the reference tests. Also, in conducting the comparison tests, the single, thin locater templet used in reference tests was used in place of the multiple thickness moveable plate means disclosed in U.S. Pat. No. 3,125,917.
The results of the first three comparison tests were found to be comparable to the results of the first three reference tests. However, when the fourth comparison test was conducted on 0.1 inch stock, using a "half-size" workpiece, it was found that the punch tips of the operative punches failed during the first press stroke; such failure being in the form of a shearing away of a portion of the cutting edge or corner of each of the operable punches, due to misalignment between such operable punches and their assorted dies. A sheared portion of the punches was left, as a deposit on the workpiece, and its presence was readily detectable by visual observation.
Failure of punches during the fourth comparison test is attributable to "cocking" or the non-parallel relationship of the guide templet relative to the die templet, during the punching operation. This results from failure of the prior patented system to provide support, i.e. clamp, to corners of the guide templet prior to compression of the stripped sleeves associated with the punches.
The reason for conducting the second and fourth tests using "half-sized" workpieces, and thus rendering only one half of the available punches operative at a given time, was to permit simulation of "multi-station" operation of the die set. In this connection, it will be understood that it is conventional to design a single die set with its punches and die elements arranged to create multiple stations, whenever it is desirable to provide for multiple hits to be performed on a single workpiece, as when the holes required to be formed in such workpiece are too close together to permit punching in a single operation, or where it is desired to punch different hole patterns in a plurality of small workpieces, which may vary in thickness, within a single press.